Method and Access Point for Assigning Sounding Resources

1. A method for assigning a sounding resource by an Access Point (AP) in a Time Division Duplex (TDD) cellular network, the method comprising: obtaining channel information between a serving AP and a User Equipment (UE) served by the serving AP; determining whether to assign the sounding resource to the UE according to a predetermined assigning criteria and based on the channel information, wherein the channel information comprises at least one of path gain information and Uplink/Downlink (UL/DL) channel quality information, and wherein the predetermined assigning criteria prioritize UEs having smaller path-loss and/or suffering/generating less UL/DL inter-cell interference; making the sounding resource assignment if it is determined to assign the sounding resource to the UE.

2. The method of claim 1 , wherein the obtaining channel information comprises obtaining channel information between the serving AP and the UE, and between interfering APs and the UE.

3. The method of claim 1 , wherein the determining comprises determining whether to assign the sounding resource to the UE according to the predetermined assigning criteria and based on the channel information and a limitation of a number of served UE able to obtain the sounding resource assignment.

4. The method of claim 1 , further comprising, if the UE is assigned the sounding resource: receiving a sounding signal sent from the UE assigned sounding resource; estimating an Uplink (UL) Channel State Information (CSI) by comparing the received sounding signal with a known original signal corresponding to the received sounding signal; calculating Downlink (DL) Beam Forming (BF) weights with the estimated CSI.

5. The method of claim 4 , wherein the sounding signal is a UL Sounding Reference Signal.

6. The method of claim 4 , wherein the calculating comprises: determining a type of BF from a plurality of BF types; calculating weights of type-determined DL BF weights with the estimated CSI.

7. The method of claim 6 , wherein the BF types comprise a non-frequency-selective BF and a frequency-selective BF.

8. The method of claim 7 , wherein the determining comprises determining, in response to the UE being assigned the sounding resource, that the type of BF is the frequency-selective BF.

9. The method of claim 1 , further comprising, if the UE is not assigned the sounding resource: estimating an Uplink (UL) Channel State Information (CSI) based on a non-sounding signal sent from the UE; calculating Downlink (DL) Beam Forming (BF) weights with the estimated CSI.

10. The method of claim 9 , wherein the non-sounding signal comprises at least one of a UL Demodulation Reference Signal (DMRS) and a UL payload data signal.

11. The method of claim 9 , wherein the calculating comprises: determining a type of BF from a plurality of BF types; calculating weights of type-determined DL BF weights with the estimated CSI.

12. The method of claim 11 , wherein the BF types comprise a non-frequency-selective BF and a frequency-selective BF.

13. The method of claim 12 , wherein the determining comprises determining, in response to the UE being assigned the sounding resource, that the type of BF is the frequency-selective BF.

14. The method of claim 12 , wherein the type of BF is determined based on at least one of: whether a latest UL Demodulation Reference Signal (DMRS) allocated bandwidth covers a DL band assignment by the serving AP; whether a time difference between a latest UL measurement and a scheduled DL BF weights utilization based on that measurement is within channel coherent time.

15. The method of claim 1 , wherein the TDD cellular network is a Time Division-Long Term Evolution (TD-LTE) network.

16. An Access Point (AP) in a Time Division Duplex (TDD) cellular network, comprising: one or more processing circuits configured to function as: an obtaining circuit configured to obtain a channel information between a serving AP and a User Equipment (UE) served by the serving AP; a determining circuit configured to determine whether to assign a sounding resource to the UE according to a predetermined assigning criteria and based on the channel information, wherein the channel information comprises at least one of path gain information and Uplink/Downlink (UL/DL) channel quality information, and wherein the predetermined assigning criteria prioritize UEs having smaller path-loss and/or suffering/generating less UL/DL inter-cell interference; an assigning circuit configured to make the sounding resource assignment if it is determined to assign the sounding resource to the UE.

17. The AP of claim 16 , wherein the obtaining circuit is configured to obtain the channel information between the serving AP and the UE, and between an interfering AP and the UE.

18. The AP of claim 16 , wherein the determining circuit is configured to determine whether to assign the sounding resource to the UE according to the predetermined assigning criteria and based on the channel information and a limitation of a number of served UE able to obtain the sounding resource assignment.

19. A computer program product stored in a non-transitory computer readable medium for assigning a sounding resource by an Access Point (AP) in a Time Division Duplex (TDD) cellular network, the computer program product comprising software instructions which, when run on one or more processing circuits, causes the one or more processing circuits to: obtain channel information between a serving AP and a User Equipment (UE) served by the serving AP; determine whether to assign the sounding resource to the UE according to a predetermined assigning criteria and based on the channel information, wherein the channel information comprises at least one of path gain information and Uplink/Downlink (UL/DL) channel quality information, and wherein the predetermined assigning criteria prioritize UEs having smaller path-loss and/or suffering/generating less UL/DL inter-cell interference; make the sounding resource assignment if it is determined to assign the sounding resource to the UE.